1. Field of the Invention
The invention is generally related to vessels used to provide offshore construction services and more particularly to a vessel that is adaptable to provide a variety of services.
2. General Background
In the production of hydrocarbons offshore, a variety of services are required. These services include laying pipeline on the sea floor and the installation of structures and equipment used in the drilling and production of hydrocarbons. The means used to lay pipeline depends upon a variety of factors such as water depth and pipe diameter. Directing the pipeline into the water at an angle nearly vertical to the water surface is typically used in deep water. This is generally referred to as J-Lay. Directing the pipeline into the water at a relatively shallow angle is typically used in shallow water. This is generally referred to as S-Lay. Each method uses different equipment to accomplish the task. J-Lay may use a near vertical support and stinger. In S-Lay, the pipe may be unwound from a reel as it is laid or pipe joints may be welded together on the laying vessel during the laying operation. Installing equipment and structures requires the use of lowering equipment such as cranes capable of handling the weight of the equipment.
Having one vessel capable of performing each operation is expensive as this can result in a vessel remaining idle when the specific operation that it is dedicated is not required. Also, current vessels dedicated to specific tasks are only capable of speeds at six to seven knots.
The current state of the art leaves a need for vessels that have multiple use capability and greater speed.
The invention addresses the above need. What is provided is a multi-use construction vessel designed to receive a variety of float-on modules that accommodate project specialty equipment and still allow the mother vessel to operate in the traditional construction mode. The vessel may be formed as a new construction or by converting an existing vessel. The vessel is provided with a lowered center section between the bow and stern. The center section is adapted to receive and secure float-on modules containing the equipment required for the desired operation. The center section may also be provided with a moon pool for laying pipeline directly through the vessel. The vessel is ballasted to position the center section below the water line so that the float-on modules may be installed or removed. The stern section of the vessel includes a derrick crane for normal construction lifts, moving pipe, and equipment on the center section as necessary.